1. Technical Field of the Invention
The present invention relates to a plate thickness reduction press apparatus that transfers and reduces a slab, and the methods concerned with its use.
2. Prior art
1. FIG. 1 shows an example of a roughing mill used for hot rolling, and the roughing mill is provided with work rolls 2a, 2b arranged vertically opposite each other on opposite sides of a transfer line S that transfers a slab-like material 1 to be shaped, substantially horizontally, and backup rolls 3a, 3b contacting the work rolls 2a, 2b on the side opposite to the transfer line.
In the above-mentioned roughing mill, the work roll 2a above the transfer line S is rotated counterclockwise, and the work roll 2b underneath the transfer line S is rotated clockwise, so that the material 1 to be shaped is caught between both work rolls 2a, 2b, and by pressing the upper backup roll 3a downwards, the material 1 to be shaped is moved from the upstream A side of the transfer line to the downstream B side of the line, and the material 1 to be shaped is pressed and formed in the direction of the thickness of the slab. However, unless the nip angle θ of the material 1 to be shaped as it enters into the work rolls 2a, 2b is less than about 17°, slipping will occur between the upper and lower surfaces of the material 1 to be shaped and the outer surfaces of both work rolls 2a, 2b, and the work rolls 2a, 2b will no longer be able to grip and reduce the material 1 to be shaped.
More explicitly, when the diameter D of the work rolls 2a, 2b is 1,200 mm, the reduction Δt of a single rolling pass is about 50 mm according to the above-mentioned nip angle θ condition for the work rolls 2a, 2b, so when a material 1 to be shaped with a thickness T0 of 250 mm is rolled, the thickness T1 of the slab after being reduced and formed by a roughing mill becomes about 200 mm.
According to the prior art, therefore, the material 1 to be shaped is rolled in a reversing mill, in which the material is moved backwards and forwards while gradually reducing the thickness of the plate, and when the thickness of the material 1 to be shaped is reduced to about 90 mm, the material 1 is sent to a finishing mill.
Another system for reducing and forming the material 1 to be shaped according to the prior art is shown in FIG. 2; dies 14a, 14b with profiles like the plane shape of dies for a stentering press machine are positioned opposite each other above and below a transfer line S, and both dies 14a, 14b are made to approach each other and separate from each other in the direction orthogonal to the direction of movement of the material 1 using reciprocating means such as hydraulic cylinders, in synchronism with the transfer of the material 1, while reducing and forming the material 1 to be shaped in the direction of the thickness of the plate.
The dies 14a, 14b are constructed with flat forming surfaces 19a, 19b gradually sloping from the upstream A side of the transfer line towards the downstream B side of the line, and flat forming surfaces 19c, 19d that continue from the aforementioned forming surfaces 19a, 19b in a direction parallel to and on opposite sides of the transfer line S.
The width of the dies 14a, 14b is set according to the plate width (about 2,000 mm or more) of the material 1 to be shaped.
However, when the material 1 to be shaped is rolled with the reversing method using the roughing mill shown in FIG. 1, space is required at each of the upstream A and downstream B ends of the transfer line S of the roughing mill, for pulling out the material 1 to be shaped as it comes out of the roughing mill, so the equipment must be long and large.
When the material 1 to be shaped is reduced and formed in the direction of its plate thickness using the dies 14a, 14b shown in FIG. 2, the areas of the forming surfaces 19a, 19b, 19c and 19d in contact with the material 1 to be shaped are much longer than those of the dies of a stentering press machine, and the contact areas increase as the dies 14a, 14b approach the transfer line S, so that a large load must be applied to each of the dies 14a, 14b, during reduction.
Furthermore, the power transmission members such as the eccentric shafts and rods for moving the dies 14a, 14b, the housing, etc. must be strong enough to withstand the above reducing loads, so each of these members and the housing must be made large in size.
Moreover, when the material 1 to be shaped is reduced and formed in the direction of its plate thickness using the dies 14a, 14b, some of the material 1 is forced backwards towards the upstream A side on the transfer line depending on the shape and the stroke of the dies 14a, 14b, therefore, it becomes difficult to transfer the material 1 to be shaped to the downstream B side of the transfer line.
When the material 1 to be shaped is reduced and formed in the direction of its plate thickness using the dies 14a, 14b shown in FIG. 2, the height of the lower surface of the material 1 after being reduced by the dies 14a, 14b is higher than the height of the lower surface of the material 1 immediately before being reduced by the dies, by an amount corresponding to the reduction in thickness.
Consequently, the leading end of the material 1 to be shaped tends to droop downwards, therefore the table rollers (not illustrated) installed on the downstream B side of the transfer line, to support the material 1 being shaped, may catch the leading end of the material 1, possibly resulting in damage to both the table rollers and the material 1 being shaped.
Recently, the flying-sizing press machine shown in FIG. 3 has been proposed.
This flying-sizing press machine is provided with a housing 4 erected on a transfer line S so as to allow movement of a material 1 to be shaped, an upper shaft box 6a and a lower shaft box 6b housed in window portions 5 of the housing 4 opposite each other on opposite sides of the transfer line S, upper and lower rotating shafts 7a, 7b extending substantially horizontally in the direction orthogonal to the transfer line S and supported by the upper shaft box 6a or the lower shaft box 6b by bearings (not illustrated) on the non-eccentric portions, rods 9a, 9b located above and below the transfer line S, respectively, connected to eccentric portions of the rotating shafts 7a, 7b through bearings 8a, 8b at the end portions thereof, rod support boxes 11a, 11b connected to intermediate portions of the upper and lower rods 9a, 9b by bearings 10a, 10b with spherical surfaces and housed in the window portions 5 of the housing 4 and free to slide vertically, die holders 13a, 13b connected to the top portions of the rods 9a, 9b through bearings 12a, 12b with spherical surfaces, dies 14a, 14b mounted on the die holders 13a, 13b, and hydraulic cylinders 15a, 15b whose cylinder units are connected to intermediate locations along the length of the rods 9a, 9b by means of bearings and the tips of the piston rods are connected to the die holders 13a, 13b through bearings.
The rotating shafts 7a, 7b are connected to the output shaft (not illustrated) of a motor through a universal coupling and a speed reduction gear, and when the motor is operated, the upper and lower dies 14a, 14b approach towards and move away from the transfer line S in synchronism with the transfer operation.
The dies 14a, 14b are provided with flat forming surfaces 16a, 16b gradually sloping from the upstream A side of the transfer line towards the downstream B side of the transfer line so as to approach the transfer line S, and other flat forming surfaces 17a, 17b continuing from the aforementioned forming surfaces 16a, 16b in a direction parallel to the transfer line S.
The width of the dies 14a, 14b is determined by the plate width (about 2,000 mm or more) of the material 1 to be shaped.
A position adjusting screw 18 is provided at the top of the housing 4, to enable the upper shaft box 6a to be moved towards or away from the transfer line S, and by rotating the position adjusting screw 18 about its axis, the die 14a can be raised and lowered through the rotating shaft 7a, rod 9a, and the die holder 13a. 
When the material 1 to be shaped is reduced and formed in the direction of the plate thickness using the flying-sizing press machine shown in FIG. 3, the position adjusting screw 18 is rotated appropriately to adjust the position of the upper shaft box 6a, so that the spacing between the upper and lower dies 14a, 16b is determined according to the plate thickness of the material 1 to be shaped by reducing and forming in the direction of plate thickness.
Next, the motor is operated to rotate the upper and lower rotating shafts 7a, 7b, and the material 1 to be shaped is inserted between the upper and lower dies 14a, 14b, and the material 1 is reduced and formed by means of the upper and lower dies 14a, 14b that move towards and away from each other and with respect to the transfer line S while moving in the direction of the transfer line S as determined by the displacement of the eccentric portions of the rotating shafts 7a, 7b. 
At this time, appropriate hydraulic pressure is applied to the hydraulic chambers of the hydraulic cylinders 15a, 15b, and the angles of the die holders 13a, 13b are changed so that the forming surfaces 17a, 17b of the upper and lower dies 14a, 14b, on the downstream B side of the transfer line, are always parallel to the transfer line S.
However, the flying-sizing press machine shown in FIG. 3 has much larger contact areas between the forming surfaces 16a, 16b, 17a and 17b of the dies 14a, 14b and the material 1 to be formed, compared to the dies of a plate reduction press machine, and because the above-mentioned contact areas increase as the dies 14a, 14b approach the transfer line S, a large load must be applied to the dies 14a, 14b during reduction.
In addition, the die holders 13a, 13b, rods 9a, 9b, rotating shafts 7a, 7b, shaft boxes 6a, 6b, housing 4, etc. must be strong enough to withstand the reducing load applied to the dies 14a, 14b, so that these members are made larger in size.
Also, the flying-sizing press machine shown in FIG. 3 may suffer from the problem that the leading and trailing ends of the material 1 being reduced and formed are locally bent to the left or right, or with a camber so that when a long material 1 is being formed it generally warps, unless the centers of the reducing forces from the dies 14a, 14b on the material 1 to be shaped are in close alignment when the material 1 is reduced and formed by the upper and lower dies 14a, 14b. 
2. With a conventional rolling mill known in the prior art, in which a material is rolled between two work rolls, there is a reduction ratio limit of normally about 25% due to the nip angle limitation. Therefore, it is not possible to reduce the thickness of a material by a large ratio (for example, reducing a material from about 250 mm thickness to 30 to 60 mm) in a single pass therefore three or four rolling mills are arranged in tandem in a tandem rolling system, or the material to be rolled is rolled backwards and forwards in a reverse rolling system. However, these systems are accompanied with practical problems such as the need for a long rolling line.
On the other hand the planetary mill, Sendzimir mill, cluster mill, etc. have been proposed as means of pressing that allow a large reduction in one pass. However, with these rolling mills, small rolls press the material to be rolled at a high rotational speed, resulting in a great impact, therefore the life of the bearings, etc., is so short that these mills are not suitable for mass production facilities.
On the other hand, various kinds of press apparatus modified from the conventional stentering press machines have been proposed (for example, Japanese patent No. 014139, 1990, unexamined Japanese patent publication Nos. 222651, 1986, 175011, 1990, etc.).
An example of the “Flying-sizing press apparatus” according to the unexamined Japanese patent publication No. 175011, 1990 is shown in FIG. 4; rotating shafts 22 are arranged in the upper and lower sides or the left and right sides of the transfer line Z of a material to be shaped, and the bosses of rods 23 with a required shape are connected to eccentric portions of the rotating shafts 22, and in addition, dies 24 arranged on opposite sides of the transfer line of the material to be shaped are connected to the tips of the rods 23; when the rotating shafts 22 are rotated, the rods 23 coupled to the eccentric portions of the rotating shafts cause the dies 24 to press both the upper and lower surfaces of the material 1 to be shaped, thereby the thickness of the material to be shaped is reduced.
However, the above-mentioned high-reduction means are associated with problems such as (1) a material to be reduced cannot be easily pressed by the flying-sizing apparatus in which the material is reduced as it is being transferred, (2) the means are complicated with many component parts, (3) many parts must slide under heavy loads, (4) the means are not suitable for heavily loaded frequent cycles of operation, etc.
With conventional high-reduction pressing means known in the prior art, the position of the dies is controlled to adjust the thickness of the material to be pressed by means of a screw, wedge, hydraulic cylinder, etc., and, as a result, there are the practical problems that the equipment is large, costly, complicated, and vibrates considerably.
3. Conventionally, a roughing-down mill is used to roll a slab. The slab to be rolled is as short as 5 m to 12 m, and the slab is rolled by a plurality of roughing-down mills or by reversing mills in which the slab is fed forwards and backwards as it is rolled. In addition, a reduction press machine is also used. Recently, because a long slab manufactured by a continuous casting system has been introduced, there is a demand for the continuous transfer of the slab to a subsequent pressing system. When a material is rough rolled using a roughing-down mill, the minimum nip angle (about 17°) must be satisfied, so the reduction limit Δt per pass is about 50 mm. Because the slab is continuous, reverse rolling is not applicable, so that to obtain the desired thickness, a plurality of roughing-down mills must be installed in series, or if a single rolling mill is to be employed, the diameter of the work rolls should be very large.
Consequently, a reduction press machine is used. FIG. 5 shows an example of such a machine in which the dies are pressed by sliders, to provide a flying-press machine that can press a moving slab. Dies 32 provided above and below the slab 1 are mounted on sliders 33, and the sliders 33 are moved up and down by the crank mechanisms 34. The dies 32, sliders 33 and crank mechanisms 34 are reciprocated in the direction of transferring the slab, by the feeding crank mechanisms 35. The slab 1 is conveyed by pinch rolls 36 and transfer tables 37. When the slab is being reduced, the dies 32, sliders 33 and crank mechanisms 34 are moved in the direction of transferring the slab by means of the feeding crank mechanisms 35, and the pinch rolls 36 transfer the slab 1 in synchronism with this transfer speed. A start-stop system can also be used; the slab 1 is stopped when the system is working as a reduction press machine and the slab is reduced, and after completing reduction, the slab is transferred by a length equal to a pressing length, and then pressing is repeated.
There are problems in the design and manufacturing cost of the aforementioned roughing-down mill with large diameter rolls, and the use of rolls with a large diameter results in a shorter life for the rolls because of the low rolling speed and difficulty in cooling the rolls. With the reduction press machine using sliders and feeding crank mechanisms shown in FIG. 5, the cost of the equipment is high because the mechanisms for reciprocating the sliders, etc., in the direction of movement of a slab are complicated and large in scale. In addition, the sliders vibrate significantly in the vertical direction. With a reduction press machine using a start-stop system, the slab must be accelerated and decelerated repeatedly from standstill to transfer speed, and vice versa. The slab is transferred using pinch rolls and transfer tables, and these apparatus become large due to the high acceleration and deceleration.
4. When a material is reduced by a large amount, according to the prior art, long dies were used to reduce the material while it was fed through the dies by the length thereof during one or several pressings. Defining the longitudinal and lateral directions as the direction in which the pressed material is moved and the direction perpendicular to the longitudinal direction, respectively, the material to be pressed by a large amount in the longitudinal direction is pressed by dies that are long in the longitudinal direction using single pressing or by means of a plurality of pressing operations while feeding the material to be pressed in the longitudinal direction. FIG. 6 shows an example of the above-mentioned reduction press machine, and FIG. 7 illustrates its operation. The reduction press is equipped with dies 42 above and below a material 1 to be pressed, hydraulic cylinders 43 for pressing down the dies 42, and a frame 44 that supports the hydraulic cylinders 43. A pressing operation is described using the symbols L for the length of the dies 42, T for the original thickness of the material 1 to be pressed, and t for the thickness of the material after pressing. FIG. 7(A) shows the state of the dies 42 set to a location with thickness T on a portion of material to be pressed next, adjacent to a portion with thickness t which has been pressed. (B) shows the state in which the dies have pressed down from the state (A). (C) is the state in which the dies 42 have been separated from the material 1 being pressed, that has then been moved longitudinally by the pressing length L, and completely prepared for the next pressing, which is the same state as (A). Operations (A) to (C) are repeated until all the material is reduced to the required thickness.
The longer the dies, the greater the force that is required for reduction, so the reduction press machine must be large. With a press machine, pressing is usually repeated at high speed. When an apparatus with a large mass is reciprocated at a high speed, a large power is required to accelerate and decelerate the apparatus, therefore the ratio of the power required for acceleration and deceleration to the power needed for reducing the material to be pressed is so large that much power is spent on driving the apparatus. When the material is reduced, the volume corresponding to the thinned portion must be displaced longitudinally or laterally because the volumes of the material before and after reduction are substantially the same. If the dies are long, the material is constrained so that it is displaced longitudinally (this phenomenon is called material flow), so that pressing becomes difficult especially when the reduction is large.
When a material to be rolled is reduced conventionally in a horizontal mill, the gap between the rolls of the horizontal mill is set so that the rolls are capable of gripping the material to be rolled considering the thickness of the material after forming, therefore the reduction in thickness allowed for a single pass is limited so that when a large reduction in the thickness is required, a plurality of horizontal mills have to be installed in series, or the material must be moved backwards and forwards through a horizontal mill while the thickness is gradually reduced, according to the prior art. Another system was also proposed in the unexamined Japanese patent publication No. 175011, 1990; eccentric portions are provided in rotating shafts, the motion of the eccentric portions is changed to an up/down movement using rods, and a material to be pressed is reduced continuously by these up/down movements.
The system with a plurality of horizontal mills arranged in tandem (series) has the problems that the equipment is large and the cost is high. The system of passing a material to be pressed backwards and forwards through a horizontal mill has the problems that the operations are complicated and a long rolling time is required. The system disclosed in the unexamined Japanese patent application No. 175011, 1990 has the difficulty that large equipment must be used, because a fairly large rotating torque must be applied to the rotating shafts to produce the required reducing force as the movement of the eccentric portions of the rotating shafts has to be changed to an up/down motion to produce the necessary reducing force.
5. Conventionally, a roughing-down mill is used to press a slab. The slab to be pressed is as short as 5 to 12 m, and to obtain the specified thickness, a plurality of roughing-down mills are provided, or the slab is moved backwards and forwards as it is pressed in the reversing rolling method. Other systems also used practically include a flying press machine that transfers a slab while it is being pressed, and a start-stop reduction press machine which stops conveying the material as it is being pressed and transfers the material during a time when it is not being pressed.
Since long slabs are produced by continuous casting equipment, there is a practical demand for a slab to be conveyed continuously to a subsequent press apparatus. When a slab is rough rolled in a roughing-down mill, there is a nip angle limitation (about 17°), so the reduction per rolling cannot be made so large. Because the slab is continuous, it cannot be rolled by reverse rolling, therefore to obtain the preferred thickness, a plurality of roughing-down mills must be installed in series, or if a single mill is involved, the diameter of the work rolls must be made very large. There are difficulties, in terms of design and cost, in manufacturing such a roughing-down mill with large-diameter rolls, and large diameter rolls must be operated at a low speed when rolling a slab, so the rolls cannot be easily cooled, and the life of the rolls becomes shorter. Because a flying press can provide a large reduction in thickness and is capable of reducing a material while it is being conveyed, the press can continuously transfer the material being pressed to a downstream rolling mill. However, it has been difficult to adjust the speed of the material to be pressed so that the flying press and the downstream rolling mill can operate simultaneously to reduce and roll the material. In addition, it has not been possible to arrange a start-stop reduction press machine and a rolling mill in tandem to reduce a slab continuously; with the start-stop reduction press, the material being pressed is stopped during pressing, and is transferred when it is not being pressed.
Another system in practical use is the flying system in which the sliders that press down on a slab are moved up and down in synchronism with the transfer speed of the slab.
In the start-stop system, the heavy slab is accelerated and decelerated every cycle from standstill to the maximum speed Vmax, and accordingly the capacity of the transfer facilities such as the pinch rolls and transfer tables must be large. Because of the discontinuous operation, it is difficult to carry out further operations on a downstream press machine. The flying system requires a large capacity apparatus to produce the swinging motion, and to accelerate and decelerate the heavy sliders according to the speed of the slab. Another problem with this system is that this large capacity apparatus for producing the swinging motion causes considerable vibrations in the press machine.
Still another problem with this system is that if the speed of the slab deviates from that of the sliders, flaws may be produced in the slab or the equipment may be damaged.
Recently, a high-reduction press machine that can reduce a thick slab (material to be pressed) to nearly ⅓ of its original thickness in a single reduction operation, has been developed. FIG. 8 shows an example of a reduction press machine used for hot pressing. With this reduction press machine, dies 52a, 52b are disposed opposite each other vertically on opposite sides of the transfer line S, and are simultaneously moved towards and away from a material 1 to be pressed that travels on the transfer line S by the reciprocating apparatus 53a, 53b incorporating eccentric axes, rods, and hydraulic cylinders, so that material of a thickness of, for example, 250 mm can be reduced to 90 mm by a single reducing operation.
However, the reduction of the aforementioned high-reduction press machine can be as large as 160 mm, that is, the reduction on one side is as large as 80 mm. According to the prior art, there is a small difference of thickness before and after pressing, so the transfer levels of the transfer devices of a press machine on the inlet and outlet sides are substantially the same. With the above-mentioned high-reduction press machine, however, there is the problem that the material 1 to be pressed is bent if the transfer levels are identical. Another problem of the machine is that the transfer device is overloaded.